First, check if it's not extensions or plugins, or some background workers a site uses (to open Chrome Task Manager, press Shift+Esc or Menu → More tools → Task Manager).
If it's not, then my guess is that this is related to hardware acceleration. But note I've not seen this cause in years, definitely not since Windows 8.
First, turn off hardware acceleration at bottom of main settings page (click Show advanced settings... at bottom of
chrome://settings, scroll to the end, un-check Use hardware acceleration when available). Recent Chrome versions ask to restart, but from my experience this option is applied immediately, at least partially.
If slowdowns didn't go away even after Chrome restart, open
chrome://flags (put this in the Chrome address bar and press Enter) and set up following:
- Disable accelerated 2D canvas – Disable
- GPU rasterization - Disable
- Hardware-accelerated video decode - Disable
- Zero-copy rasterizer - Disable
(that was for Chrome 53.0.2785.89, other options may be available on older systems, where Chrome does not update, for example:
- Disable DirectWrite - Enable
- Enable one-copy rasteriser - Disabled
- Enable zero-copy rasteriser - Disable
- Disable hardware-accelerated video decode – Enable
then click Relaunch now at bottom of the window.
If everything will become fine (but a little slower overall maybe), you can switch options back to default one by one until you find one causing the trouble.
(if you won't find an option in flags list, skip it. Maybe also look for other options about GPU and hardware acceleration and make sure HW acceleration and GPU usage are disabled. Chrome gets updates quite often, and flags get added and removed in almost each version).
Answers to the questions:
Is there a way to reduce the amount of CPU usage by Chrome?
when I click on the plus button on the top to open a few new windows it causes the video/audio to lag. <…> Any idea why this is happening?
only guesses. Either Extension or plugin may cause this, or adding another layer to composited window causes videodriver lag (composited – window with several layers, and some of them rendered by hardware, for example, by hardware video decoding). This is why I suggested to turn off hardware acceleration and check.
Aren't these pages supposed to be kept in their separate processes?
they are kept indeed, but there is one main process (per profile) which outputs information to window. If this process halts for some reason, window updates will stop, and it will look like Chrome isn't responding. I guess, sound output is also done via that main process, this is why sound also lags.
You can check process tree with Process Explorer.
Why the difference between opening them in another profile and in the same profile?
Flags, Extensions and Plugin setting are per-profile, and Extensions off by default in Incognito mode. This is why it may behave differently with different profiles (even with single main chrome process).